DE 103 34 000 A1 describes a trailer coupling for a tractor vehicle, with a coupling head for attaching a coupling counterpart of a trailer vehicle, a coupling shaft which is connected to the tractor vehicle and which, in the area of the coupling head, defines a vertical axis, and an angle sensor which is integrated in the trailer coupling and which registers movement of the coupling counterpart relative to the coupling shaft about the vertical axis. The coupling head is mounted so that by virtue of a roller bearing arranged in the coupling head, it can rotate relative to the coupling shaft about the vertical axis. In this case, the friction of the roller bearing is negligibly small compared with the friction between the coupling head and the coupling counterpart.
Mounting by means of a roller bearing is relatively elaborate. In particular, owing to the small diameter of the coupling head only little structural space is available for integrating the roller bearing, which as a rule comprises many moving parts, in the coupling head, which has to withstand large forces during trailer towing operation and can therefore only be made smaller to a limited extent at acceptable cost. Furthermore, roller bearings are also sensitive to point loading that often occurs during trailer towing operation, so that such bearings undergo premature wear.